1. Field of the Invention
The present invention relates to an electro-conductive member to be used as a charging member or the like in an electrophotographic apparatus, an electrophotographic apparatus, and a process cartridge.
2. Description of the Related Art
A material formed of an ionic electro-conductive rubber composition has been known as a constituent material for the electro-conductive elastic layer of an electro-conductive member to be used in an electrophotographic apparatus. The elastic layer formed of such material has advantages in that the voltage dependence of its electrical resistance is small and a variation in its electro-conductivity is small. Japanese Patent No. 03540278 discloses an electro-conductive rubber roller using an ionic electro-conductive rubber composition containing, at a predetermined ratio, a terpolymer formed of ethylene oxide (EO)-propylene oxide (PO)-acrylic glycidyl ether (AGE), and an acrylonitrile-butadiene rubber (NBR).
However, an investigation on the electro-conductive rubber roller according to Japanese Patent No. 03540278 conducted by the inventors of the present invention has revealed that an elastic layer formed of the electro-conductive rubber composition containing the EO-PO-AGE terpolymer and the NBR has high moisture absorption property and the shape of the electro-conductive rubber roller changes owing to moisture absorption particularly under a high-humidity environment in some cases. Accordingly, when such electro-conductive roller is used as a charging roller, a variation in its charging performance resulting from the change of its shape may occur.